Steam generator for convection oven

ABSTRACT

A steam generator for use in a convection oven comprising a plurality of first and second spherically shaped heat accumulator elements arranged alternately in a substantially vertical plane in which the first layer contains at least one row of the heat accumulating elements integrally joined together at a central axis and the second layer contains at least two rows of the heat accumulating elements integrally joined together at a central axis, and a convection oven employing the steam generator are disclosed.

This is a division of application Ser. No. 08/176,791, filed Jan. 3,1994 now U.S. Pat. No. 5,394,791.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a steam generator for use in a convection ovensuch as that used in a commercial bakery; and to a heat accumulator unitwhich forms part of the steam generator.

2. Prior Art

When bread is baked in a convection oven in which the bread is contactedwith circulating heated air, it is known to introduce steam or watervapor into the oven chamber for a brief period at the beginning of thebaking process to impart a desired color and crispness to the crust ofthe bread.

In Swiss Pat. No. 532,363, water is sprayed on the walls of steamingchambers heated by circulated air to form steam within the oven chamber.

Swiss Pat. No. 548,161 discloses a steam generator which utilizes anindependent heater for the steam generator.

In U.S. Pat. No. 2,767,667, a conveyorized oven has a steaming unitlocated at the entrance to a conveyor and uses a steam generator whichis remote from the conveyor or conveyor housing to provide steam fordirect application to the bread. There is a fan for circulating thesteam over the entering bread remote from the conveyorized baking areaof the convection oven.

U.S. Pat. No. 4,202,259 discloses a nonconveyorized convection oven suchas a rack oven which employs a steam generating device outside the ovenchamber and which needs no secondary fan for forcing circulation, butwhich is capable of vaporizing water without the use of any auxiliaryheater. The steam generator is described as containing a multiplicity ofblocks, which may be in the form of metal balls. The multiple blocks areloosely disposed along a linear channel and heated by circulating heatedair. At the beginning of the baking process, water is sprayed onto theblocks where a portion of the water is vaporized while the remainderflows through a slot opening and is distributed over the blocksimmediately below.

One of the disadvantages of the steam generator described in U.S. Pat.No. 4,202,259 is that the metal balls are loosely disposed in thegenerator which makes the generator inconvenient to assemble and repairsince loose balls may escape and roll across the factory or bakeryfloor.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a steamgenerator for use in a convection oven which is more efficient and whichis capable of rapidly vaporizing relatively large amounts of waterwithout use of an external heating device and which is convenient toassemble and repair.

It is another object of the invention to provide a convection ovencontaining a steam generator which has improved baking capabilities.

It is yet another object of the invention to provide a heat accumulatorunit for use in a steam generator which is convenient to store, ship andassemble.

The steam generator in accordance with the invention comprises aplurality of first and second heat accumulator units arrangedalternately in a substantially vertical plane, said first heataccumulator unit containing at least one horizontal row of heataccumulator elements and said second heat accumulator unit containing atleast two horizontal rows of heat accumulator elements.

In accordance with a preferred embodiment of the invention, the steamgenerator further comprises a plurality of perforated baffleshorizontally disposed between every other heat accumulator unit suchthat a perforated baffle is located immediately above every first heataccumulator unit and immediately below every second heat accumulatorunit;

water supply means at the top of said steam generator for spreadingwater onto said heat accumulator elements;

cover unit for covering said water supply means;

a base unit located at the bottom of said steam generator, said baseunit including means for collecting and draining excess water from saidsteam generator; and

a pair of horizontally spaced apart side panels extending verticallybetween said base unit and said cover unit for supporting said heataccumulator unit and said baffles, said panels being fixed to oppositeends of said base unit and at corresponding ends of said cover unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of an oven embodying the steamgenerator of the invention.

FIG. 2 is a perspective view of the steam generator of the invention ina partially exploded view.

FIG. 3 is a vertical cross-sectional view of the steam generator of theinvention taken along line A--A of FIG. 2.

FIG. 4 is a perspective view of a first horizontal unit of heataccumulator elements of the present invention.

FIG. 5 is a plan view of a first horizontal unit of heat accumulatorelements of the present invention.

FIG. 6 is a side view of a first horizontal unit of heat accumulatorelements of the present invention.

FIG. 7 is a perspective view of a second horizontal unit of heataccumulator elements of the present invention.

FIG. 8 is a plan view of a second horizontal unit of heat accumulatorelements of the present invention.

FIG. 9 is a side view of a second horizontal unit of heat accumulatorelements of the present invention.

FIG. 10 is an enlarged sectional view of a heat accumulator unit of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The principles of the steam generator of the present invention areparticularly useful when embodied in a convection oven. In a typicaloperation of a convection oven containing the steam generator of thepresent invention, the oven is pre-heated to a predetermined temperaturefor a period of time to allow the steam generator to reach a peaktemperature for vaporizing water into steam. The bread or other goods tobe baked are loaded onto a wheeled rack and placed in the oven chamberand the oven door is closed. The rack is then lifted off the floor by alifting device and begins to rotate at a set speed. The steaming processis started by spraying water over the heat accumulating units to producesteam uniformly over the total height of the steam generator. The steamproduced infiltrates the entire oven and condenses on the cool surfaceof the unbaked bread or other goods. At the end of the predeterminedsteaming period (about 10 to 30 seconds), the flow of water to the steamgenerator is discontinued and the bake cycle started. During the bakeperiod a fan continuously circulates the heated air throughout theentire system. For additional batches, the procedure is repeated exceptthat it is generally not necessary to pre-heat the oven since theprevious baking cycle provides sufficient heat.

As shown in FIG. 1, a typical oven 10 in accordance with the inventionhas a chamber 12 including an apertured upstream side 14 and a partiallyapertured downstream side 16. Disposed within the chamber 12 is a rack18 connected at its upper end to a rotatably driven carrier 20 carriedby a vertical shaft 22. The rack 18 can be raised and lowered by a shiftmechanism (not shown) located on the upper end of the shaft 22. Watervapor is absorbed by the heated air from the steam generator 26 which isshown in FIG. 2 and circulated throughout the oven chamber 12 in aclosed path by a fan 24. Goods to be baked such as bread 56 are placedin pans held by rack 18 which rotates to uniformly expose the bread 56to the heated, steam-containing air as it flows through the oven chamber12.

The steam generator 26 is disposed outside the oven chamber andcomprises a base 28 above which are located a plurality of heataccumulator units 30. The base 28, which contains a receptacle 29 and adrain pipe 32, serves as a sump for collecting and draining away anyexcess water accumulated during the steam forming process. The heataccumulator units 30 are held in place by end panels 54 verticallyaffixed to each end of the base 28 and to the corresponding ends of thesteam generator cover 48. Steam generator cover 48 includes deflectorplates which slope downwardly and inwardly. Where the steam generator 26is of sufficient size to accommodate or require two or more of the heataccumulator units 30 in a head-to-tail arrangement, support panels 34are vertically affixed to the base 28 and to the cover 48 intermediatethe two end panels 54 to support the heat accumulator units 30.

The heat accumulator units 30 comprise a first horizontal unit 30Acontaining heat accumulator elements 36 which are joined to each otherforming a linear horizontal row; and a second horizontal unit 30B ofheat accumulator elements 36 joined to each other as in the firsthorizontal unit 30A. Horizontally disposed baffles 42 containingmultiple perforations 44 are placed below each second horizontal unit30B to aid in the distribution of water to the heat accumulator elements36, and to uniformly accumulate steam from the top to the bottom of thesteam generator 26. The first horizontally disposed unit 30A and thesecond horizontally disposed unit 30B are illustrated as having two rowsand three rows of heat accumulator elements 36, respectively. While 2rows and 3 rows, respectively are the preferred number of rows for thefirst and second horizontal units, it is within the scope of theinvention for the first horizontal unit 30A to contain X number of rowsand for the second horizontal unit 30B to contain a number of rows equalto X+1, where X is about 1 to 3.

Each of the heat accumulator units 30A and 30B comprises a plurality ofheat accumulator elements 36 having a spherical shape. The sphericallyshaped elements 36 are integrally joined together along a central axisin a linear configuration to form the heat accumulator units 30A and30B. In a preferred aspect of the invention, the heat accumulator unitsare cast from a thermally conductive metal such as cast iron using amold having the desired shape and dimensions.

Each of the heat accumulator units 30A and 30B are illustrated in FIGS.2 and 3 as consisting of two separate units joined together in ahead-to-tail relationship with each of the separate units having alength which accommodates eleven heat accumulator elements. Such unitsare easily assembled and disassembled. While individual units ofrelatively short dimensions are preferred for the purpose of shippingand handling of the individual components of the steam generator 26, itis to be understood that the heat accumulator units 30A and 30B mayconsist of longer single units as well as a multiplicity of shorterunits. The number of heat accumulator elements 36 present in the heataccumulator units 30A and 30B is not critical, however, for practicalpurposes each accumulator unit is about 12 to 18 inches in length andpreferably about 15 inches in length, and the number of heat accumulatorelements 36 of each heat accumulator unit 30 is preferably about 10 to12 with each element 36 being about 1 to 1.5 inches in diameter, andpreferably about 1.25 inches in diameter.

Just prior to the bake cycle, water is provided to the steam generator26 through apertures 46 in water supply line 52. The water sprayed fromaperture 46 is deflected by the sides of steam generator cover 48 anddirected downwardly to contact the rows of heat accumulator elements 36.As the water contacts the heat accumulator elements 36, the accumulatedheat in the elements 36 is sufficient to transform the water into vaporalong the entire height of the steam generator 26. During the steamingcycle (about 15 to 30 second), the fan 24 is stopped to avoid loss ofsteam in the oven air duct. The moisture-containing air is introduceddirectly through the apertured downstream side wall 16 and uniformlycontacts and condenses on the unbaked and cold bread 56. When the steamcycie is finished, the fan 24 is activated again and the heat exchanger50 reheats the moisture-laden air. At the beginning of the bake cycle,the fan is activated causing the air flowing through the partiallyapertured downstream side wall 16 to reheat the steam generator for thenext bake as it flows freely between the rows of heat accumulator units30. The heated, moisture-containing air is circulated through the ovenchamber until the baking process has been completed, at which time thebaked goods are removed and the oven loaded with another batch to bebaked.

The heat accumulator units 30 are illustrated in more detail in FIGS.4-9. In FIGS. 4-6, the heat accumulator unit represents a first (orupper) heat accumulator unit 30A which contains two rows of heataccumulator elements 36 joined to each other in a linear configuration.In FIGS. 7-9, the heat accumulator unit represents a second (or lower)heat accumulator unit 30B which contains three rows of heat accumulatorelements 36 joined to each other in a linear configuration.

FIG. 10 is an enlarged section illustrating the attachment of heataccumulator elements 36 to each other in the linear configuration.

The steam generator shown in the drawings is only an exemplaryembodiment and, it is to be understood that the invention is not solimited and that changes may be made therein without departing from thescope of the invention which is defined in the appended claims.

What is claimed is:
 1. A steam generator for use in a convection ovencomprising a plurality of vertically stacked first and second heataccumulator units arranged alternately in a substantial vertical plane,said first heat accumulator unit containing a pair of end blocks havingat least one linear row of spherically shaped heat accumulator elementsextending between said end blocks, the spherically shaped elements ineach row of said first heat accumulator unit being integrally joinedtogether and fixed relative to each other along a horizontal axis andsaid second heat accumulator unit containing a pair of end blocks havingat least two linear rows of spherically shaped heat accumulator elementsextending between said end blocks, the spherically shaped elements ineach row of said second heat accumulator unit being integrally joinedtogether and fixed relative to each other along a horizontal axis,wherein said first heat accumulator unit can be vertically stacked onsaid second heat accumulator unit by setting said end blocks of saidfirst heat accumulator unit on said end blocks of said second heataccumulator unit wherein said generator includes a pair of vertical sidepanels, said side panels having a pair of horizontally extending flangeswherein said end blocks are contained in said side panels between saidflanges.
 2. The steam generator of claim 1 wherein said first heataccumulator unit contains two linear rows of heat accumulator elementsand said second heat accumulator unit contains three linear rows of heataccumulator elements.
 3. The steam generator of claim 1 wherein saidgenerator further comprises:a plurality of perforated baffleshorizontally disposed between every other heat accumulator unit suchthat one of said perforated baffles is located immediately above everyfirst heat accumulator unit and immediately below every second heataccumulator unit; water supply means at the top of said steam generatorfor spreading water onto said heat accumulator elements for generatingsteam; a cover unit for covering said water supply means; a base unitlocated at the bottom of said steam generator, said base unit includingmeans for collecting and draining excess water when generating steam;and a pair of horizontally spaced apart side panels extending verticallybetween said base unit and said cover unit for supporting said heataccumulator units and said baffles, said panels being fixed to oppositeends of said base unit and fixed to opposite ends of said cover unit. 4.The steam generator of claim 3 wherein said water supply means includesa tubular pipe containing a plurality of apertures, said tubular pipebeing connected to a source of water.
 5. The steam generator of claim 4wherein said plurality of apertures are formed bilaterally along saidwater supply tubular pipe and said cover means includes deflector plateswhich slope downwardly and inwardly defining a longitudinal openingcentrally above a first layer of heat accumulator elements, wherein saiddeflector plates direct said water to said heat accumulator elements. 6.The steam generator of claim 1 wherein said spherically shaped heataccumulator elements have a diameter of about 1 to 1.5 inches.
 7. Thesteam generator of claim 6 wherein said diameter is about 1.25 inches.8. The steam generator of claim 1 wherein said first and said secondheat accumulator units are cast from a thermally conductive material. 9.The steam generator of claim 8 wherein said material is cast iron. 10.The steam generator of claim 1 wherein said generator furthercomprises:water supply means at the top of said steam generator forspreading water onto said heat accumulator units; a base unit located atthe bottom of said steam generator, said base unit including means forcollecting and draining excess water from said steam generator.
 11. Asteam generator for use in a convection oven comprising:a plurality offirst and second heat accumulator units arranged alternately in asubstantially vertical plane, said first heat accumulator unitcontaining two linear rows of spherically shaped heat accumulatorelements, the spherically shaped elements in each row of said first heataccumulator unit being integrally joined together and fixed relative toeach other along a horizontal axis and said second heat accumulator unitcontaining three linear rows of spherically shaped heat accumulatorelements, the spherically shaped elements in each row of said secondheat accumulator unit being integrally joined together and fixedrelative to each other along a horizontal axis; a plurality ofperforated baffles horizontally disposed between every other heataccumulator element such that a perforated baffle is located immediatelyabove every first heat accumulator unit and immediately below everysecond heat accumulator unit; water supply means at the top of saidsteam generator for spreading water onto said heat accumulator units; acover unit for covering said water supply means; a base unit located atthe bottom of said steam generator, said base unit including means forcollecting and draining excess water from said steam generator; and apair of horizontally spaced apart side panels extending verticallybetween said base unit and said cover unit for supporting said heataccumulator units and said baffles, said panels being fixed to oppositeends of said base unit and at corresponding ends of said cover unit. 12.The steam generator of claim 11 wherein said water supply means includesa tubular pipe containing a plurality of apertures, said tube beingconnected to a source of water.
 13. The steam generator of claim 12wherein said plurality of apertures are formed bilaterally along saidtubular pipe and said cover unit includes deflector plates which slopedownwardly and inwardly defining a longitudinal opening centrally abovethe heat accumulator elements, wherein said deflector plates direct saidwater to said heat accumulator units.
 14. The steam generator of claim11 wherein said heat accumulator units are cast from a thermallyconductive material.